1. Field of the Invention
This invention relates to semiconductor laser devices and, more particularly, to a semiconductor laser device which is applicable for disc players, barcode readers, etc.
2. Description of the Prior Art
In general, the active layer includes an optical waveguide which at ends undergoes oxidation to have a band gap reduced smaller than that of a central position, resulting in absorption of laser light and rise in temperature. Due to this, catastrophic optical damage (hereinafter referred to as xe2x80x9cCODxe2x80x9d) tends to occur more readily at the end portions of the optical waveguide than in a central position thereof. There is a fear that such COD might cause deterioration in characteristic of the semiconductor laser device.
In order to prevent this, it has been a conventional practice to adopt a method to allow laser light to permeate from an end portion of an optical waveguide into a cladding layer, thereby reducing the photon density therein. Furthermore, another method has also been utilized wherein zinc (Zn) is thermally diffused into the end portions of an optical waveguide thereby obtaining transparent regions (NAM structure). Thus the optical waveguide at its ends has been suppressed from being raised in temperature.
Of the above-mentioned prior arts, the method of lowering the photon density involves a problem that the emission efficiency of laser light be lowered. On the other hand, in the method of forming an NAM structure, there is difficulty in exactly controlling the Zn diffusion depth, thus resulting in instability of characteristic. Moreover, there has been a problem that the manufacture process becomes complicated by the necessity of such processes as forming a Zn-containing film, removing the same film, thermally diffusing Zn, and so on.
Therefore, it is a primary object of the present invention to provide a semiconductor laser device which can prevent COD without incurring reduction in tight emitting efficiency or complication in manufacture process.
A semiconductor laser device according to the present invention, including a lower cladding layer, an active layer having an optical waveguide, an upper cladding layer and an upper electrode which are overlaid a substrate, to inject an electric current from the upper electrode through the upper cladding layer into the active layer, comprises: a current non-injection region provided at an end portion of the active layer.
The current non-injection region can be provided by forming an insulation film on a contact layer in a position corresponding to an end portion of the active layer and between the upper electrode and the upper cladding layer. The insulation film may be typically formed of an insulation material, such as SiO2, Al2O3, or Ti2O3. The insulation film, in concrete, can be formed by a organic metal chemical vapor deposition method.
The insulation film formed between the upper electrode and the upper cladding layer acts to block a leak current from flowing from the upper electrode to the end portion of the active layer. Accordingly, no current is injected to the end portion of the active layer, thereby providing a current non-injection region at the end portion. The current non-injection region at the end of the active layer is free from temperature rise due to Joule""s heat and hence band gap decrease due to such temperature rise.
According to the present invention, no band gap decrease occurs at the end of the optical waveguide. Thus, it is possible to suppress against temperature rise due to laser light absorption and hence COD. Also, there is no necessity to permeate laser light into the cladding layer or to form a Zn-containing film. Hence, light emission efficiency is not lowered and manufacture process is not complicated.